A coaxial cable is a transmission line which has two conductors, each having the same axis, with one conductor surrounding the other conductor and being insulated therefrom by suitable dielectric material. Coaxial cable transmits or receives high or low power radio frequency signals up to and including millimeter wave frequencies. Such signals are used in a wide variety of fields including communications, medical equipment, temperature measurement, etc. Coaxial cable may be in three classifications, namely rigid, semirigid or flexible. A typical coaxial cable in simplified form is comprised of a center conductor surrounded by a dielectric layer which in turn is surrounded by an electrically conductive outer jacket. The center and outer conductors are generally high conductivity metallic materials.
It is known to connect coaxial cable with circuit components for providing frequency filters or time delays. A typical low-pass filter has one or more conductive discs concentric with a center conductor and surrounded by a dielectric sheet which is in turn surrounded by an electrically conductive outer jacket. Such circuit components are prefabricated as separate elements which are then mechanically and electrically coupled to adjacent ends of coaxial cables. The present invention includes recognition of various inherent disadvantages in using such prefabricated circuit components including problems in impedance matching at the joints between the circuit components and the coaxial cables, high manufacturing costs, inability to accurately tune the circuit components after assembly, limited power handling due to an air film between the dielectric material surrounding the circuit components and the ID of the outer jacket, the practical limit on the diameter of the cable when making small diameter coaxial cable, the lack of a radially continuous dielectric layer surrounding the circuit components, etc.
The present invention is directed to coaxial cable and the method of making the same so as to avoid the disadvantages set forth above while having other advantages as will be made clear hereinafter.